Unprofessional and Irresponsible

So I'm helping out a customer at the tech counter who is purchasing a computer.  His check got declined so he is calling up his bank to find out if he went over his limit or is there a problem because he just spent a grand at Sleepy's.  So while he's on the phone instead of just sitting there tapping my fingers I looked at some of the computers that were in for service.  While I'm looking up something on our computer my manager calls over to me from the ink section and asks me to look up the ink for a particular model.  She gives me the model and I look it up on our website.  I find the right ink and tell her which one she needs.  I go back to the guy buying the computer who says he is going to make one more call.  So I let him make the call and go back to our computer to look for a driver for a computer.  Then all hell breaks loose.  The lady the manager was helping starts flipping out.

"THIS IS DISGUSTING!!! THIS IS IRRESPONSIBLE AND UNPROFESSIONAL!!!! I WANT TO SPEAK TO THE MANAGER NOW!!!!" 

The manager then explains that she is the manager but the lady is not happy she wants her manager's phone number who is our DM Lord Farquaad.  At this point I honestly have no idea what is going on but I really don't want to get involved. But as the manager is in the office calling the DM to explain the situation the lady is waiting at the tech counter while the guy is still on phone and I'm at the tech computer. I try to avoid all interaction with this lady but of course she has to vent to me as well.

"I am just sick of this store.  I have nothing but problems here.  I bought a computer here and overpaid $100 and it took 30 days for it to come back to me and then there were problems with the computer that Dell had to switch out parts." BLAH BLAH BLAH

As I'm still on the computer I was about to ask her how we overcharged her $100 on a computer but I decided I really didn't care and would rather not have this lady yell at me too.

So the reason this lady was flipping out was because we didn't have the color cartridges for her older printer.  It is available online but it is not in the store because we recently had a remodel and we can't carry every cartridge ever made. It is not our fault what we carry or don't carry in our store, this is the decision of the corporate office who by the way are apparently just little toy monkeys with tamborines (or at least this what I picture when we talk about the corporate office).   I found out about this when I was near the office and the manager was all pissed off because Lord Farquaad told her to give her a new printer and new ink.  The key word being GIVE not sell.  Apparently this was STILL not good enough for this lady she didn't want to lug the printer home even though the manager offered to bring it to her car.  She said she'll just take her laptop to her friends house and use their printer because this is so inconvient.  Some people are so stupid and maybe if you didn't wait last minute to buy your ink we could have ordered it online and you would have had it.